Exploring, drilling and completing hydrocarbon and other wells are generally complicated, time consuming and ultimately very expensive endeavors. As a result, over the years well architecture has become more sophisticated where appropriate in order to help enhance access to underground hydrocarbon reserves. For example, as opposed to wells of limited depth, it is not uncommon to find hydrocarbon wells exceeding 30,000 feet in depth. Furthermore, in order to ensure efficiency of well operations, an added amount of emphasis may be placed on initial well evaluations, as well as subsequent monitoring and more direct interventions throughout the life of the well.
From the outset of operations, complex logging applications utilizing sophisticated electronic components may be run in the well in order to establish an initial overall profile of the well. Additionally, subsequent interventions may be run to complete and manage the well over time. These interventions may range from the complex installation of completions equipment to more abrupt perforating interventions as part of stimulating operations and a host of other intervention types as well.
In the case of logging applications, sensitive electronic components are utilized that generally include some form of heat related protection. For example, a logging tool may include a heat sensitive board and various pressure, temperature and other sensors that would be susceptible to failure upon direct exposure to extreme heat. Indeed, it is not uncommon for the majority of such components to be rated to effectively operate in temperatures that are under about 200° C. (or 400° F.). However, once the tool reaches a depth of several thousand feet, which is generally expected in today's wells, temperatures may exceed 400° F. or more. Thus, as noted above, such heat sensitive components are sometimes afforded heat related protection in the form of flasking.
Heat sensitive components of a logging tool, or any downhole tool, may be housed within a flask. A flask is a structure that includes a heat sink type of casing about the tool or component that is configured to absorb heat from the surrounding environment. The flask will generally also include insulation located about the heat sink to serve as an outer shield to the heat. Flasking heat sensitive components in this manner serves to delay failure-level heat from reaching the heat sensitive components for hours. That is, an application may be run and completed before the heat sensitive components are ever actually exposed to a level of heat sufficient to effect component failure.
Flasking in the manner described above is usually most effective where a Dewar type flasking is utilized. This means that the heat sink may be retained within a multi-walled structure which itself surrounds the heat sensitive component or tool. This allows the heat sink to be of a highly effective phase change material. For example, as opposed to a solid stainless steel or other more static material, the heat sink may be of a bismuth-based or other suitable phase change material which moves from a solid to a more liquid form as heat is absorbed. Phase change materials such as these have been established as extremely effective in absorbing heat and protecting underlying heat sensitive components from the more extreme temperatures of the well.
Unfortunately, utilizing a solid to liquid phase change material as described for the heat sink means that a new risk of exposure is now presented to underlying sensitive tool components. Specifically, the risk of exposing the sensitive components to a melting wax-like substance or other liquid is now presented. As noted, this means that the multi-walled Dewar-type flask is needed to retain the heat sink material. However, this presents a host of manufacturability challenges, for example, when keeping in mind the needed wiring into and out of the flask to reach the protected components. Indeed, a sophisticated manufacturing process of wiring, filling and sealing the multi-walled Dewar structure with the heat sink material may be required. In today's dollars, for a conventional 5-10 foot logging tool, this may translate into well over $40,000 dedicated to flasking alone.
Even more problematic than the expensive flasking for a reusable logging tool as described above is the circumstance where such flasking is desired for a single use application. For example, where the heat sensitive component at issue is a detonator of a perforating gun to be used once and then destroyed during the perforating application, the most effective flasking option detailed above remains generally impractical due to the costs involved. Nevertheless, the attempt may be undertaken due to the hazardous nature of the application where failure potentially results in premature detonation. Unfortunately, while such efforts are often less than reliable the costs are also quite high as noted above.